Evolution of structural and magnetic properties of Ar2+ ion irradiated TiO2 thin films annealed under argon atmosphere

Abstract

In this report, the evolution of structural as well as magnetic state of 900 °C annealed TiO2 films under argon (Ar) environment have been examined before and after irradiating with the Ar2+ ions of energy 500 keV. The pristine film stabilized with Magneli phase (Ti4O7), the film retains its crystallinity but phase get transformed to anatase TiO2, irradiating with the lowest fluence, 1 × 1014 ions/cm2. After rising up to 5 × 1016 ions/cm2 ion fluence, film again stabilize with the Magneli phase (Ti4O7). In the previous report, we have demonstrated an unusual phase change from anatase TiO2 to brookite, where films are annealed in O2 atmosphere. In contrast to that here we have obtained TiO2 from Ti4O7 at lowest fluence but at highest fluence again Ti4O7 is obtained. The energy deposited by the ion beam passed to the lattice and collision cascades are formed which brings atomic displacement in the lattice, results the structural transformation. Surface topography is not affected much after the irradiation as observed from atomic force microscopy (AFM). Interesting, ferromagnetic behavior at room temperature stems in all the films as a consequence of the controlled introduction of anionic defects (oxygen vacancies).